EXALTONE.RTM. and muscone, two macrocyclic ketones, are very appreciated in the art for their elegant and tenacious musky odour. Both compounds have been known for several decades and since their discovery a variety of syntheses have been proposed and described in the scientific literature [see: e.g. J. Chem. Soc. 1964, 4154; Tetrahedron 20, 2601 (1964); Helv. Chim. Acta 50, 705 (1967) and Helv. Chim. Acta 50, 708 (1967)]. So far, however, most of the published methods could not be successfully applied to their industrial scale preparation, especially in view of their complexity or in view of the low yields achieved in the critical reaction steps.
One of the prior known syntheses [Helv. Chim. Acta 50, 705 (1967)] is making use of the compound of formula ##STR3## (R=H; n=zero in formula I) as intermediate in the synthesis of EXALTONE.RTM. (cyclopentadecanone), and of the corresponding methyl derivative of formula ##STR4## (R=methyl; n=zero in formula I) in the synthesis of muscone. Both intermediate compounds can be obtained from cyclododecanone, by a condensation reaction and a subsequent cyclization, hydrogenation and dehydration. Due to rather poor overall yields, however, such synthetic routes do not present any major interest to the industry.
The merit of the invention consists in proposing a new and original synthetic process for preparing the above mentioned intermediate compounds, by making use of cheap and easily available starting materials, viz. the bicyclic compounds of formula (II): 13-oxa-bicyclo[10.4.0]hexadec-l(12)-ene e.g. (R=H in formula II) is also used as starting material for preparing EXALTOLIDE.RTM. [see in this respect DE-PS No. 2,026,056 and DE-AS No. 2,065,551].